Identifying o/s rear axle area LHM leak

[AdrianO]

I don't normally have a problem identifying the source of a LHM leak, but this one has me puzzled.

Leak seems to happen only after (as?) the car sinks fully down over a day or so, which would indicate a low pressure return issue. But the only candidate I can see is the flexible pipe that emerges from the underside of the rear axle (not sure if I have identified that part correctly), as per the attached pic. This pipe is loose at the point of exit (the corresponding pipe on the n/s is not). However the spread of LHM extends over the axle, which suggests the source of the leak could be higher up. Yet the only pipe I can identify in that vicinity is the rigid brake LHM feed pipe - but this leak does not seem happen when the engine is running.

Any thoughts would be appreciated.

rear axle area leak

[Kitch]

If you suspect a brake line, it will only leak when you press the pedal (your original post worded it like you'd only had a look while engine was running). Could be a union?

[Jaba]

Its most likely to be the rubber Tee which connects the returns from the two rear suspension cylinders. It is tricky to see but it sits above the axle tube on the offside and is where the 2 clear plastic return pipes connect to another pipe which goes forward to the front of the car.
Its easier to write that than it is to find and see it.
You can improvise a replacement with a plastic Tee and using rubber pipe to connect to the 3 plastic return tubes.

[rutter123]

Agreed with Jaba on that, the rubber t piece breaks up as mine did, you can use rubber windscreen washer tubing and connectors which your local motor factors should have a selection of,

[AdrianO]

Following those suggestions I've had another butcher's, this time with the rear wheel off. I can confirm it's not a hard pipe/union issue. On the other hand, I can't definitely confirm it's the tee piece return either, as I could neither see nor feel the damn thing. (Does one drop the fuel tank or the trailing arm for access LOL?). However, the upper part of the axle tube and the vicinity does appear to be free of LHM. Hmmm.

Something I didn't mention in the o/p was that I wiped off the leakage and performed the citerobics shuffle - no immediate leakage was apparent. The leakage itself is evidently slow and small, I'd guess averaging in the order of 2ml per day - I've had larger ones from LHM returns before.

I'm therefore suspecting the other flexible pipe from the suspension - presumably the vent pipe - clearly visible in my pic where it enters the axle tube. I'm supposing that the rear strut design is similar to the front strut in that the vent pipe should connect to the system returns and not hang loose, so to speak. I'm back with the observation that at the o/s where the leak is, the vent pipe is not secure into the axle tube; but on the n/s rear suspension the corresponding pipe is secure. It's obvious at the front strut where the vent pipe connects, but where does the rear vent pipe connect?

[rutter123]

Check the steel brake lines especially where they are clamped to the rear beam, there is a small bracket/clamp held with a 10mm headed bolt, the old steel pipes can corrode at this point as the pipe bends at 90 degrees just there. It will only show signs of the smallest amount of fluid loss through a pinholed pipe. Don't force the bolts or they WILL break soak them with some penetrating fluid overnite.

[barry badger]

If it,s the y piece chevronics do it, it's the larger bore orange one, i've just ordered one for my 4x4. I noticed the leak when i had the ruptured sphere problem. I fitted a second hand one i had but it was rock hard and split as i was fitting it.

[AdrianO]

Check the steel brake lines especially where they are clamped to the rear beam, there is a small bracket/clamp held with a 10mm headed bolt, the old steel pipes can corrode at this point as the pipe bends at 90 degrees just there. It will only show signs of the smallest amount of fluid loss through a pinholed pipe. Don't force the bolts or they WILL break soak them with some penetrating fluid overnite.

I had the front-to-back rigid pipes replaced a couple of years ago. Curiously, it was at the bracket you mention on the near side where one of them had failed. IIRC that leak was ongoing with the engine off, but visibly worse with the engine on. I'm not (yet, anyway) seeing that symptom here.

[Jaba]

The rear suspension vent pipes are just that, they vent air into the rear axle tube and normally do not ever leak LHM.
That Tee we are mentioning sits above the axle tube and you get to it from the front of the axle. It is possible to pull it down a bit for inspection. Sometimes there is a cable tie which holds it in position on one of the suspension return pipes.

The plastic return pipes can wear through where they pass through the eye of the suspension rod retaining clip.

Also the rear height corrector can leak from its diaphragm as well as the rubber return pipe.

[AdrianO]

Well waddayouknow. Today the leak seems to have stopped. I cleaned all the pipework, checked the brackets and clips - all sound. I will wait to see how things develop (MOT next month).

However, I did establish that the n/s vent pipe is not actually secured internally to the axle cylinder, so that situation is the same on both sides. The o/s vent pipe still seems to me proximate origin of the leak, notwithstanding that the vent pipes should not (by design?) leak LHM. Clearly the front and rear hydraulic arrangements differ in a way I don't fully comprehend.

Many thanks to everyone who contributed suggestions. It's good that The Knowledge is around even as BX's go to the Great Scrapyard In the Sky.